Minimally invasive surgery (“MIS”) techniques reduce the amount of extraneous tissue that are damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. It is estimated that 7,000,000 surgeries performed each year in the United States can be performed in a minimally invasive manner. However, only about 1,000,000 of the surgeries currently use these techniques, due to limitations in minimally invasive surgical instruments and techniques and the additional training required to master them.
Advances in minimally invasive surgical technology could have a dramatic impact. The average length of a hospital stay for a standard surgery is 8 days, while the average length for the equivalent minimally invasive surgery is 4 days. Thus the complete adoption of minimally invasive techniques could save 24,000,000 hospital days, and billions of dollars annually in hospital residency costs alone. Patient recovery times, patient discomfort, surgical side effects, and time away from work are also reduced with minimally invasive surgery.
The most common form of minimally invasive surgery is endoscopy. A common form of endoscopy is laparoscopy, which is minimally-invasive inspection and surgery inside the abdominal cavity. In standard laparoscopic surgery, a patient's abdomen is insufflated with gas, and cannula sleeves are passed through small (approximately ½ inch {1 cm.)) incisions to provide entry ports for laparoscopic surgical instruments.
The laparoscopic surgical instruments generally include a laparoscope for viewing the surgical field, and working tools, such as clamps, graspers, scissors, staplers, and needle holders. The working tools are similar to those used in conventional (open) surgery, except that the working end of each tool is separated from its handle by an approximately 12-inch long extension tube.
To perform surgical procedures, the surgeon passes instruments through the cannula and manipulates them inside the abdomen by sliding them in and out through the cannula, rotating them in the cannula, levering (i.e., pivoting) the instruments in the abdominal wall and actuating end effectors on the distal end of the instruments. The instruments pivot around centers of rotation approximately defined by the incisions in the muscles of the abdominal wall. The surgeon observes the procedure by a television monitor, which displays the abdominal worksite image provided by the laparoscopic camera.
Similar endoscopic techniques are employed in arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy, cystoscopy, cistemoscopy, sinoscopy, hysteroscopy and urethroscopy. The common feature of all of these minimally invasive surgical techniques is that they generate an image of a worksite within the human body and pass specially designed surgical instruments through natural orifices or small incisions to the worksite to manipulate human tissues and organs, thus avoiding the collateral trauma caused to surrounding tissues, which would result from creating open surgical access.
There are many disadvantages of current minimally invasive surgical technology. First, the video image of the worksite is typically a two-dimensional video image displayed on an upright monitor somewhere in the operating room. The surgeon is deprived of three-dimensional depth cues and may have difficulty correlating hand movements with the motions of the tools displayed on the video image. Second, the instruments pivot at the point where they penetrate the body wall, causing the tip of the instrument to move in the opposite direction to the surgeon's hand. Third, existing MIS instruments deny the surgeon the flexibility of tool placement found in open surgery. Most laparoscopic tools have rigid shafts and are constrained to approach the worksite from the direction of the small incision. Those that include any articulation have only limited maneuverability. Fourth, the length and construction of many endoscopic instruments reduces the surgeon's ability to feel forces exerted by tissues and organs on the end effector of the tool.
Overcoming these disadvantages and achieving expertise in endoscopic procedures requires extensive practice and constant familiarization with endoscopic tools. However, despite surgeons' adaptation to the limitations of endoscopic surgery, the technique has brought with it an increase in some complications seldom seen in open surgery, such as bowel perforations due to trocar or cautery injuries. Moreover, one of the biggest impediments to the expansion of minimally invasive medical practice remains lack of dexterity of the surgical tools and the difficulty of using the tools.
In a tangentially related area, telesurgery systems are being developed to increase a surgeon's dexterity as well as to allow a surgeon to operate on a patient from a remote location. ‘Telesurgery” is a general term for surgical systems where the surgeon indirectly controls surgical instrument movements rather than directly holding and moving the tools. In a system for telesurgery, the surgeon is provided with an image of the patient's body at the remote location. While viewing the three-dimensional image, the surgeon manipulates a master device, which controls the motion of a servomechanism-actuated slave instrument, which performs the surgical procedures on the patient. The surgeon's hands and the master device are positioned relative to the image of the operation site in the same orientation as the slave instrument is positioned relative to the act. During the operation, the slave instrument provides mechanical actuation and control of a variety of surgical instruments, such as tissue graspers, needle drivers, etc., which each perform various functions for the surgeon, i.e., holding or driving a needle, grasping a blood vessel or dissecting tissue.
Such telesurgery systems have been proposed for both open and endoscopic procedures. An overview of the state of the art with respect to telesurgery technology can be found in “Computer Integrated Surgery: Technology and Clinical Applications” (MIT Press, 1996). Prior systems for telesurgery are also described in U.S. Pat. Nos. 5,417,210, 5,402,801, 5,397,323, 5,445,166, 5,279,309 and 5,299,288.
Proposed methods of performing telesurgery using telemanipulators also create many new challenges. One is presenting position, force, and tactile sensations from the surgical instrument back to the surgeon's hands as he/she operates the telesurgery system, such that the surgeon has the same feeling as if manipulating the surgical instruments directly by hand. For example, when the instrument engages a tissue structure, bone, or organ within the patient, the system should be capable of detecting the reaction force against the instrument and transmitting that force to the surgeon. Providing the instrument with force reflection helps reduce the likelihood of accidentally damaging tissue in areas surrounding the operation site. Force reflection enables the surgeon to feel resistance to movements of the instrument when the instrument engages tissue. A system's ability to provide force reflection is limited by factors such as friction within the mechanisms, gravity, the inertia of the surgical instrument and the size of forces exerted on the instrument at the surgical incision. Even when force sensors are used, inertia, friction and compliance between the motors and force sensors decreases the quality of force reflection provided to the surgeon.
Another challenge is that, to enable effective telesurgery, the instrument must be highly responsive and must be able to accurately follow the rapid hand movements that a surgeon may use in performing surgical procedures. To achieve this rapid responsive performance, a surgical servomechanism system must be designed to have an appropriately high servo bandwidth. This requires that the instrument have low inertia. It is also preferable if the system can enhance the dexterity of the surgeon compared to standard endoscopic techniques by providing more degrees-of-freedom (“DOFs”) to perform the surgery by means of an easily controlled mechanism. By more DOFs, it is meant more joints of articulation, to provide more flexibility in placing the tool end point.
Another challenge is that to enable minimally invasive surgery, the instrument must be small and compact in order to pass through a small incision. Typically MIS procedures are performed through cannulas ranging from 5 mm. to 12 mm. in diameter.
Surgeons commonly use many different tools (sometimes referred to herein as end-effectors) during the course of an operation, including tissue graspers, needle drivers, scalpels, clamps, scissors, staplers, etc. In some cases, it is necessary for the surgeon to be able to switch, relatively quickly, from one type of end effector to another. It is also beneficial that effectors be interchangeable (even if not very quickly), to reduce the cost of a device, by using the portion of the device that does not include the end effector for more than one task.
However, the mass and configuration of the effector affects the dynamics and kinematics of the entire system. In typical cases, the effector is counter balanced by other elements of the system. Thus, to the extent that effectors are interchangeable, this interchangeability feature should be accomplished without rendering the remainder of the system overly complicated.
What is needed, therefore, is a servomechanical surgical apparatus for holding and manipulating human tissue under control of a teleoperator system.
It would also be desirable to provide a servomechanical surgical apparatus that can provide the surgeon with sensitive feedback of forces exerted on the surgical instrument.
It would further be desirable to provide a servomechanical surgical apparatus that is highly responsive, has a large range of motion and can accurately follow rapid hand motions that a surgeon frequently uses in performing surgical procedures.
It would still further be desirable to provide a servomechanical surgical apparatus that increases the dexterity with which a surgeon can perform endoscopic surgery, such as by providing an easily controlled wrist joint.
It would also be desirable to provide a dexterous surgical apparatus having a wrist with three independent translational degrees-of-freedom, which can provide force feedback with respect to those three degrees of freedom.
It would still further be desirable to provide a surgical instrument having a wrist mechanism for minimally invasive surgery, which is suitable for operation in a telemanipulator mechanism.
It would additionally be desirable to provide a servomechanical surgical apparatus that has easily interchangeable end effectors, the exchange of which does not require significant adjustments to the kinematic and dynamic control of the apparatus, thereby allowing different end effectors to be used on one base unit, either during the same operation, or, at least, during different operations.
To some extent, the inventions discussed in the three patent applications by the present inventors Madhani and Salisbury that are incorporated herein by reference, address these goals. The invention described herein further satisfies these goals.